Did you make this instructable?

I believe you cannot convert them. I am no battery expert but with past conversations with a friend it is in the way they are constructed, the materials and thickness of the plates. Car batteries are made to be cheap (sort of). Regular LAs will deep cycle to a point, just not as deep and won't tolerate as many deep charges. But if you have some left overs that are sitting go ahead and use them before they die of old age.

CHEAP!?!?!?CHEAP!?!?!?!?!?CRAZYYYYYYYY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!, NOPE THIS IS NOT MADNESS! THIS IS SPARTA! THIS IS SPARTA! THIS IS SPARTA! THIS IS SPARTA! THIS IS SPARTA! THIS IS SPARTA! THIS IS SPARTA! (credit goes to GorillazMiko)